1. Field of the Invention
This invention relates to novel DNA sequences encoding a polypeptide termed Neuritin, which is expressed primarily in certain brain tissues in response to certain stimuli.
2. Related Art
A number of neurological disorders and diseases are caused at least in part by degeneration or death of particular classes of neurons. For example, Parkinson's disease is characterized by slowing of voluntary muscle movement, muscular rigidity, and tremor. Such symptoms are attributed at least in part to progressive degeneration of dopamine-producing neurons located in a specific region of the brain called the substantia nigra. Degeneration of these neurons ("dopaminergic neurons") results in a decrease of dopamine levels in an adjacent region of the brain called the striatum. The striatum contains neurons expressing receptors for dopamine; these neurons are involved in the control of motor activity. The cause of the degeneration of dopaminergic neurons is unknown, but has been attributed to free radicals, excess iron content, environmental toxins, excitatory amino acid neurotoxicity, and possibly a deficiency of certain neurotrophic factors (Jenner, Neurology, Suppl. 3:S6-S12 1995!; Adams and Victor, eds. Principles of Neurology, Chapter 42: Degenerative Diseases of the Nervous System, McGraw Hill, N.Y. 1993!).
Diseases such as amyotrophic lateral sclerosis (ALS), progressive muscular atrophy, and hereditary motor and sensory neuropathy (Charcot-Marie-Tooth disease) all result at least in part from a decay of motor neurons which are located in the ventral horn of the spinal cord.
The hippocampus, a well defined structure that is part of the cerebral cortex of the brain, is important in the formation of long term memory. Destruction of the hippocampus, for example by ischemia, can result in an inability to form new memories. Degeneration of pyramidal CA1 neurons, which are located in the CA1 region of the hippocampus, is one characteristic of Alzheimer's disease. These same neurons are selectively vulnerable to ischemic and anoxic damage which occur in conditions such as stroke and head trauma. In addition, the CA1 pyramidal hippocampal neurons as well as pyramidal neurons located in the CA3 region of the hippocampus, are selectively injured in epilepsy.
The striatum is the innervation region of the nerve terminals of dopaminergic-containing neurons from the substantia nigra. The majority of striatal neurons utilize GABA (4-aminobutyric acid) as their neurotransmitter. The striatum is the major target of the progressive neurodegeneration that occurs in Huntington's disease, in which the major neuron loss is that of the striatal GABA-utilizing neurons.
The serotonin-containing neurons are located in groups clustered around the midline of the hindbrain. These neurons are involved in the control of body temperature, mood, and sleep. Disorders of the serotonin-containing neuron system include, for example, depression, other mood disorders, and sleep disturbances.
Photoreceptor cells are a specialized subset of retina neurons, and are responsible for vision. Injury and/or death of photoreceptor cells can lead to blindness. Degeneration of the retina, such as by retinitis pigmentosa, age-related macular degeneration, and stationary night blindness, are all characterized by the progressive atrophy and loss of function of photoreceptor outer segments which are specialized structures containing the visual pigments that transform a light stimulus into electrical activity.
While there are some therapies available to treat the symptoms and decrease the severity of such diseases (e.g., L-dopa to treat Parkinson's disease), there currently exists no effective treatment to prevent or reduce the degeneration of most of the above mentioned classes of affected neurons, or to promote their repair.
Recently, several naturally occurring proteinaceous molecules have been identified based on their trophic activity on various neurons. These molecules are termed "neurotrophic factors". Neurotrophic factors are endogenous, soluble proteins that can regulate survival, growth, and/or morphological plasticity of neurons (see Fallon and Laughlin, Neurotrophic Factors, Academic Press, San Diego, Calif. 1993!).
The known neurotrophic factors belong to several different protein superfamilies of polypeptide growth factors based on their amino acid sequence homology and/or their three-dimensional structure (MacDonald and Hendrikson, Cell, 73:421-424 1993!). One family of neurotrophic factors is the neurotrophin family. This family currently consists of NGF (nerve growth factor), BDNF (brain derived neurotrophic factor), NT-3 (neurotrophin-3), NT-4 (neurotrophin-4), and NT-6 (neurotrophin-6).
CNTF (ciliary neurotrophic factor) and LIF (leukemia inhibitory factor) are cytokine polypeptides that have neurotrophic activity. By virtue of their structural features and receptor components, these polypeptides are related to a family of hematopoietic cytokines that includes IL-6 (interleukin-6), IL-11 (interleukin-11), G-CSF (granulocyte-colony stimulating factor), and oncostatin-M.
GDNF (glial derived neurotrophic factor) is a neurotrophic factor that belongs to the TGF-beta (transforming growth factor beta) superfamily. GDNF displays potent survival and differentiation-promoting actions for dopaminergic and motor neurons (Lin et al., Science, 260:1130-1132 1993!; Yan et al., Nature, 373:341-344 1995!).
While these neurotrophic factors are known to increase growth and/or survival of neurons, there is less known about the molecules that work in conjunction with these factors. One manner in which additional neurotrophins and related molecules may be identified is to administer to an animal one or more compounds known to have an effect on the nervous system, and to then analyze tissues for the induction of genes involved in neural responses to the compounds. For example, one can screen for genes that are induced in certain tissues of the nervous system, such as the hippocampal region of the brain. This technique was used by Nedivi et al (Nature, 363:718-722 1993!; Nedivi et al., Proc. Natl. Acad. Sci USA, 93:2048-2053 1996!) to identify novel genes that are induced in the dentate gyrus portion of the hippocampus in response to administration of a neurotransmitter analog of glutamate called kainate (kainic acid).
Expression of many neurotrophic factors such as NGF, BDNF, NT3, GDNF, bFGF, IGF-1 and TGF-beta are regulated by afferent neuronal activity and/or by neuronal injury. Strong induction of some of these genes can be observed in the hippocampus dentate gyrus in response to the glutamate analog kainate (Isackson, Current Opinions in Neurobiology 5:50-357 1995!). Kainate treatment appears to increase the release of novel compounds from the hippocampus of alert rats, and this activity appears to be different from the actions of known neurotrophic factors (Humpel, et al., Science, 269:552-554 1995!).
In view of the fact that many nervous system disorders and diseases have no known cure, there is a need in the art to identify novel compounds for treating neurological conditions and diseases such as Parkinson's disease, amyotrophic lateral sclerosis (ALS), Alzheimer's disease, stroke, and various degenerative disorders that affect vision.
Accordingly, it is an object of the present invention to provide novel compounds that may be useful in promoting neuron regeneration and restoring neural functions.
It is a further object of the invention to provide a method of treating certain neurological diseases.
These and other objects will be apparent to one of ordinary skill in the art from the present disclosure.